The present invention is directed to a system for locating an agricultural vehicle wherein signal quality information from two position sensors is evaluated and used to calculate the position of the vehicle by weighting the position signals.
WO 94/24845 A and U.S. Pat. No. 6,128,574 disclose an automatically steering system for agricultural vehicles wherein the system locates the vehicle on the basis of their immediate position and an intended target path. The position is determined from a location system by means of a satellite system (GPS or DGPS). So that in the case of a failure of the satellite signal the location system can continue to be operated further, U.S. Pat. No. 6,128,574 provides that the utility vehicle be equipped with operating direction sensors and velocity sensors. Furthermore, both references propose that the signals of the satellite system be supplemented by sensors attached to the utility vehicle, that can detect, for example, the crop edge or windrow of the crop being harvested. For this purpose the crop edge orientation system can be provided, according to WO 94/24845 A, in the form of an image operating system or, according to U.S. Pat. No. 6,128,574, a reflex location system (such as, for example, a laser scanner) or a harvested edge orientation system relying on mechanical touching.
Currently, the local direction of operation sensor and the local velocity sensor are used only upon a failure of the satellite system, while the harvested edge sensors are used continuously in order to improve the accuracy of the position signal. But there are cases in which a satellite signal is available, but whose accuracy is not sufficient due to errors in the propagation time caused by near-by obstacles in order to guide the utility vehicle with sufficient precision. It is also conceivable that the accuracy of the local sensor used for the recognition of the boundaries of the stand of the crop is not adequate, in order to use its position signal to improve the accuracy of the position signal derived from the satellite signal. Cases of this type cannot be avoided by the known automatic steering systems.
It is an object of the present invention to provide an improved location system for determining the position of an agricultural vehicle, that is distinguished by high accuracy even under unfavorable conditions.
The first position signal and the second position signal are generated by separate sensors independent of one another. These sensors generate first and second position signals that are communicated to a controller. At least one of the position signals contain signal quality information that is also communicated to the controller. The quality information is directed to the accuracy of the respective position signal. The controller evaluates the signal quality information and develops a weighting factor used to calculate the position of the harvesting machine based on the first and second position signals. If the quality information points to a high degree of accuracy of the first position signal, the first is considered exclusively or at least to a large proportion in the calculation of the position. The second position signal is considered only in a small proportion or not at all. Analogously the first position signal is ignored or considered only to a small degree, if the quality information points to a low degree of accuracy of the first position signal. With an approximately median accuracy of the first position signal, the first and the second position signals can be considered with equal weight.
In this way the actual position is determined in an exact and reliable way by consideration of the particular measurement accuracy of at least one of the position signals. The invention can be used in connection with an automatic steering arrangement, but also, for example, in order to generate position signals for yield mapping.
In a preferred embodiment the controller is supplied with quality (accuracy) information about both position signals. The controller also uses this information in order to establish which position signal is considered to which degree.
The first position signal is usually a signal generated by satellite signals that can be generated, for example, by means of a corresponding antenna that interacts with the GPS (global positioning system) or another satellite system. But the employment of an inertial navigation system is also conceivable.
The second position signal can be generated by a local sensor on the agricultural vehicle. The local sensor can detect the movement of the utility vehicle (direction of operation and velocity). Alternatively, or in addition, the local sensor is a sensor that detects the position of the vehicle relative to a stationary object, particularly the operational boundary or a crop edge. Sensors of this type are sufficiently well known in the form of an image processing operating system, laser scanning sensors, or mechanical scanning arrangements for the detection of rows of crop as they are already used for automatic steering of agricultural machines. There is also the possibility of using a laser distance sensor in which the transmitter and/or the receiver is not rotated, but a mirror rotating continuously or step-by-step is used to scan the visible region. It can scan an angular region of up to 180xc2x0. Sensors of this type are available from Sick A.G. D-72796, Reute, under the designation LMS. Sensors for the measurement of the width of cut on cutter heads can also be used.
The invention is preferably applied to an arrangement for the automatic steering of an agricultural vehicle. The controller is provided with a memory in which is stored a target path for the vehicle. The target path defines the path the vehicle is to follow in a selected operation. The controller generates a steering signal on the basis of the position calculated from the position sensors and target path information stored in the memory. The controller generates a steering signal that is communicated to a steering controller.
Furthermore it is proposed to use the quality information for the selection of the target path information from several possible target path possibilities. Corresponding to the accuracy information about the position signal of one of the position sensors, that can be derived from the quality information, the appropriate target path information is selected, which can best be combined with the position signal of the position sensor. For example, it is conceivable to steer the vehicle, in the case of sufficient accuracy of a position signal that interacts with a stationary object, for example, a crop edge along the object (operating boundary). In this case the target path information corresponds to the intended position of the vehicle relative to the boundary of operation. A digital map generated in advance of the area to be operated upon is not required. If the quality information points to the fact that the accuracy of this position signal is not adequate or is no longer adequate, then the evaluation arrangement can derive the target path information automatically from the path previously covered (in the form of a learning operation) from corresponding position information recorded in the form of a map. The steering is then performed on the basis of a signal of the other position sensor. The target path information now corresponds to the map that defines the path to be covered. If it is found later on the basis of the quality information that the position signal defining the boundary operation is again sufficiently accurate, the latter can again be used for the steering of the utility vehicle. Analogously it is conceivable to steer the utility vehicle on the basis of satellite information with a map stored in memory and in the case of a failure of the satellite signal to use a sensor of the boundary (crop edge) and a velocity sensor to generate the steering signal. It becomes possible generally to use as target path information not necessarily a map stored in advance that is costly to generate, but information that is easily obtained, for example, the desired position of a boundary of operation or an information about a path previously covered.